Flashcards in Pulm. Function Tests Deck (41):
Pulmonary function tests include:
- Spirometry with FEV 1
- FEV 25-75
- flow volume loops
- V/Q scan
- pulse ox
- SaO2 from ABG
- mixed venous O2
- sat from Pa cath
What should mixed venous sat be?
If lower—> increased O2 consumption or not getting enough O2
What are indications for PFTs?
- possible pneumectomy or lobectomy
- surgery of upper abdomen
- hx of pulm dz
- severe obesity
- pickwickian syndrome
- evidence of pulm. Dysfunction during physical exam (DOA) ** dyspnea at rest is a sign of bad pulm dysfunction
What is pickwickian syndrome?
Combo of conditions:
- decreased pulm. Function
What PFT values indicate high risk?
- FEV1 < 2L
- FEV1/FVC < 0.5
- VC <15ml/kg (adult) 10 mL/kg (child)
- VC <40-50% than predicted (usually 80%)
What does obtaining PFTs preoperatively help with?
Estimates pulmonary reserve to better plan pre, intra, and post op. Pulm care requirements
How do you optimize a pt preoperatively?
- bronchodilators *most important** >15% improvement in FEV1 after 1 tx
- CHF: (with rales)diuretics the night before
- antibiotics: sputum c and s
How do you optimize a pt intraoperatively?
- emphysema requires longer “E” time on vent
- closely monitor PIP—> emphysematic blebs can rupture
- CO2 retainers: keep CO2 near baseline (may be 50-60)
-rapid correction leads to met. Alkalosis
- CO2 retainers have high HCO3 too
- Bronchospasm: ***avoid histamine releasing drugs*** (morphine)
- tx. With nebulized albuterol
What’s the best way to give neb. Albuterol intraop.?
Vent. Inline T piece—> use O2 10L/min to run
- give proposal to make up for diluted agent
How do you optimize a pt post-operatively?
Make sure they meet proper extubation criteria:
- VSS, awake and alert, RR <30
- ABG on Fio2 40%:
- PaO2 >70
- PaCO2 <55
-MIF (Max inspiratory force) more negative than -20cmH2O
- VC >15mL/kg
How do you obtain MIF?
Obstruct airway during inhale, see how negative a force they can generate
What are the different FEV1 ranges and their predictions during extubation?
-FEV1 >50%—> extubation probably not effected
- FEV1 25-50%—> some hypoxemia and hypercarbia
- prolonged intubation probable
- FEV1 <25%—> only life saving procedures should be done
- regional anesthesia if possible
- long term vent support
- inability to wean possible
- Trach. Probable
What are the criteria for acute resp failure?
** KNOW WHEN TO INTUBATE ** (no one every got sued for putting in a tube)
- mechanics: RR > 35, VC <15mL/kg, MIF more negative that -20mmHg
- oxygenation: PaO2 <70 on Fio2 40%
- A-a gradient >350 mmHg on 100% O2
- ventilation: PaCO2 >55% (except when chronic).
- Vd/Vt >0.6 (normal dead space is 30%)
- clinical: airway burn (intubate sooner, before edema), chemical burn, epiglottitis, Mental status changes, fatigue, rapidly deteriorating pulm status
What will a CXR show with pleural effusions?
Blunted costophrenic angles
Why get an expiratory CXR?
Heart looks wider
Best to view pneumothorax
- less air (black on x-ray) in lungs so more can be seen
What do you do if pneumothorax is seen on CXR?
Consult thoracic surgeon for chest tube
- give 100% FiO2
- s/s include JVD, tachycardia, hypotension
What do you do if a tension pneumo is seen on CXR and how can you tell?
right heart border is gone: lung tension is pushing on it
- treat immediately! —> needle decompress
- mid claviclular line
- then get chest tube
What does CHF look like on CXR?
What does RUL consolidation signify on a CXR?
- wont’ see it right away
- after aspiration, get baseline CXR anyway
How long do you have to run an ABG?
15 min—> or glycolysis will occur, with lactic acid production, decreased pH and increased CO2
- can be stored on ice for 1-2 hours
Which pressure correlates best with arterial pressure?
Brachial pressure coming off pump
What are ABG norms?
- pH: 7.35-7.45
- PCO2: 35-45 mmHg
- PO2: 75-105 mmHg
- HCO3: 20-26 mmoles/L
- BE: -3 to +3 (0)
What are some buffers in the blood?
Substances that can absorb or donate H+
- serum proteins
- phosphate (HPO4)
What is true regarding CO2 and pH?
An increase of PCO2 by 10mmHg causes a decrease in pH by 0.08
Can the body buffer acidosis or alkalosis better?
What is the difference between hypoxemia and hypoxia?
Hypoxemia: decreased O2 in blood, < 70
Hypoxia: a low O2 state
How do you calculate PaO2?
(Pb - PH2O) x (FiO2) - (PaCO2/0.8)
Normal PaO2 on room air (.21)= 100
What is a normal A-a gradient?
Widens during anesthesia with intrinsic lung dz
(Pneumo, shunt. V/Q mismatch)
Is the A-a gradient normal in hypoventilation or low FiO2?
Yes, just treat with supplemental O2
- adjust vent and PEEP, treat underlying cause
How does bicarbonate affect pH?
A decrease in HCO3 by 10 mmoles, decreases the pH by 0.15
And vice versa
Total bicarbonate deficit=
Base deficit x wt in kg x 0.4
—> usually replace 1/2 of deficit in mEq/L
(Good equation to use in trauma pt)
What causes respiratory acidosis?
Low pH, high CO2
* hypoventilation and hypercarbia
- CNS depression
- decreased FRC
- airway obstruction
- COPD, asthma, pulm fibrosis
* after 1-2 days kidneys reabsorb HCO3
—-> partially corrects, not completely
What causes respiratory alkalosis?
High pH, lowCO2
*hyperventilation with hypocarbia
- hypoxic respiration
- CNS disease/encephalitis
- narcotic W/D
- early septic shock
- hypermetabolic states
- artificial ventilation
—> kidneys compensate by excreting HCO3 and H+
- both partially correct alkalosis
What are causes for metabolic alkalosis?
High pH, high HCO3
- bicarbonate infusion
- metabolism of lactate or citrate
- loss of H+ from vomiting or NGT auctioning
—>resp compensation limited—> hypoventilation - can only hypoventilate so much
- kidneys may increase HCO3 secretion
What causes metabolic acidosis?
Low pH, low HCO3
- lactic acidosis from hypoperfusion, DKA, renal dz with HCO3 loss, diarrhea (especially in kids), ASA ingestion, high protein intake
—> resp compensation- with hypercarbia (central chemoreceptors)
- resp faster than kidneys—> increase H+ excretion
What is FEV1?
* the most important clinical tool in assessing severity of obstructive disease *
FEV1= after max inspiration, the volume of air that can be forcefully expelled in 1 second
- normally 3-5L
-can be reported as % of FVC
- FEV1/FVC—> normallly >75%
What degree of obstruction lung dz risk do these values of FEV1/FVC represent?
>75, 60-75, 45-60, 35-45, <35
60-75—> mild Lung dz
45-60—> moderate lung dz
35-45—> severe lung dz
<35—-> extreme lung dz
What do flow volume loops do?
Help distinguish upper airway from lower/generalized pulm dz
- Extrathoracic (upper airway obstruction)= decreased insp. Flow
- intrathoracic (lower airway obstruction)= decreased expiratory flow
What does FEV 25-75 measure?
Forced expiratory flow at 25-75% of FVC
- effort independent
- sensitive indication of early airway obstruction
- reflects collapse of small airways and peripheral airways
What is the MVV or MBC test?
The will to live test
- max amount of air pt can exhale in 1 minute at maximum effort (hyperventilation)
- tests motivation, mechanics, strength, endurance
* a decrease predicts increased morbidity and mortality in pts undergoing thoracic surgery